Extract numbers from a list

Hi~

There is A=[1:1:37] in matlab, two numbers are randomly drawn from the list A simultaneously, and a total of 74 times are drawn. Requires are as fllows:

1. Each number is drawn 4 times in total.

2. And the same number will not appear twice every time you draw

3. The same number will not be drawn for two consecutive trials.

The final result is expressed as a 74×2 list, each row represents an extraction, the first column indicates the first number drawn, and the second column indicates the second number drawn.

[Stephen23]

It looks like you will need a WHILE loop, or something similar. What have you tried so far?

[Jane]

I have tried:

"drawnNumbers = datasample(fullList, 2, 'Replace', false);"

I wonder know how to fufill the reqirement 2?

[Stephen23]

"I wonder know how to fufill the reqirement 2?"

By specifying "Replace"=false you have already fulfilled requirement 2.

[Jane]

I misread it just now, it should be requirement three.

[Stephen23]

"I misread it just now, it should be requirement three."

You could make a sample, then test if its elements are different compared to the last sample. If the values are duplicated make another sample (e.g. a WHILE loop).

However you should be thinking about requirement 1, because how you approach that will determine the entire structure of your algorithm and code, probably more than requirements 2 and 3.

[Jane]

Yes, very sensible~

Answer 1

[Bruno Luong]

succeed = false;
while ~succeed
    c = repelem(4,37,1);
    n = sum(c);
    r = rand(1,n);
    y = [];
    for i=1:n
        cn = c;
        cn(y) = 0;
        cc = cumsum(cn);
        s = cc(end);
        succeed = s > 0;
        if ~succeed
            break
        end
        x = discretize(r(i), [0; cc/s]);
        r(i) = x;
        c(x) = c(x)-1;
        y = r(max(i-mod(i,2)-1,1):i);
    end
end
r = reshape(r,2,[])';
r

r = 74×2

15 22 9 13 22 2 11 35 1 26 25 20 19 4 22 25 17 13 23 22

[Jane]

Fabulous! Thanks a lot.

[Bruno Luong]

You are welcome.